1. Field of the Invention
This invention relates to methods and apparatus for feeding granular and powdery type materials to receptacles for storage of such materials prior to processing the materials upon removal from the receptacles. Specifically, this invention relates to methods and apparatus for feeding granular plastic resin materials and additives for granular plastic resin materials to receptacles for storage temporarily in the receptacles prior to removal of the resin materials for processing by plastic molding and extrusion machinery.
2. Description of the Prior Art
In the plastics industry automatic material conveying has been used for many years with vacuum being a common means for such conveying.
Blowers are sometimes used to provide positive pressure conveying. In blower-driven systems, cyclone separators separate air from conveyed plastic resinous material prior to delivery to the material to a final delivery point.
However, vacuum is the preferred means for such conveying. Vacuum systems tend to be cleaner, producing less dust than blower-driven, positive pressure systems.
As a part of a vacuum system it is known to provide a vacuum supply unit as an integral unit, with a vacuum source, the material receptacle and controls for the supply system all combined in a single package. These are inexpensive systems and are similar to conventional home vacuum cleaners and to vacuum cleaners sold under the trademark “Shop-Vac” to do-it-yourself home hobbyists. In the industrial context such units may be mounted over a resinous material storage receptacle requiring filling with resinous material. Such units sell for from $600.00 to $2,000.00 in the industrial context.
More sophisticated and better vacuum material loading systems are referred to as “central” systems. Such central systems typically sell for $2,000.00 or more per receptacle or station being loaded and can control from 5 to 40 or more receptacles or loading stations.
In vacuum systems it is known to use cloth filters to filter plastic resinous material from air streams moving towards vacuum pumps. The cloth filters typically become clogged rather quickly, requiring frequent maintenance and replacement. Cloth filters also wear quickly from granular plastics material impact and abrasion.
Existing devices use blow-back techniques to clear the filter between material supply cycles. These blow back devices add cost and complexity to the system.
Some vacuum loading apparatus use wire screens to keep out large particles, thereby allowing small dust particles to move towards the vacuum pump. A large general filter can provide filtering for many or all of the receptacles at once.
It is known to use timers to time the loading of plastic resinous material into receptacles or loading stations. Conventionally, individual timers are used for each loading station with the timers being preset in advance to control loading.